Formation of mechanical joints between electrical conductors



Unitsd States Patent Ivor Manning, Sutton Coldfield, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Application February 19, 1957 Serial No. 641,012

6 Claims. (Cl. 29-15555) No Drawing.

This invention relates to an improved method of making mechanical joints between electrical conductors.

The formation of efiicient mechanical joints between conductors formed from metals or alloys which tend to form a natural oxide skin on exposure to the atmosphere involves the removal of the oxide skin, which has a high electrical resistivity, and exclusion-of air from the deoxidised mating surfaces while the joint is being made. 7 The formation of a natural oxide skin is particularly marked in the case of aluminium and aluminium base alloys and various methods have been used hitherto to overcome its effects on the efiiciency of conductor joints, including scratch brushing under Vaseline, tinning with solders, electroplating, and metal spraying, but none of these methods is entirely satisfactory from the point of view of electrical conductivity, stability during service, cost, or case of application.

I have developed a greatly simplified method of joint formation between electrical conductors of which at least one is formed from metal or alloy liable to form a natural oxide skin on exposure to the atmosphere, in which the materials involved are relatively inexpensive and which produces a joint of excellent electrical efiiciency. This method consists in applying a jointing composition consisting of an aqueous emulsion of an inorganic fluorinecontaining compound which has an acidic reaction in solution, a wetting agent, and a soap, to one or both of the mating surfaces and assembling the conductors in joint relationship so that the said composition is between the said surfaces.

As suitable fluorine-containing substances there may for example be mentioned hydrogen fluoride, the bifluorides (MHF boron trifiuoride, fluoboric acid (HBF and derivatives thereof yielding an acidic reaction in aqueous solution. The amount of fluorine containing substance present may be varied within fairly wide limits which will depend upon the particular substance selected. The minimal amounts are however determined by the provision that to be effective the pH of the composition must not be greater than 5.

As wetting agents there may for example be mentioned the higher acyl derivatives of hydroxyor amino-alkyl sulphonic acids, salts of monosulphuric esters of higher fatty alcohols, alkyl derivatives of aromatic sulphonic acids. The amount of wetting agent in the composition may also be varied within wide limits, but there should be at least a suificient quantity present to enable the composition to spread evenly over the mating surface of the conductor and to give thorough wetting thereof.

The soaps comprise salts of the saturated and unsaturated fatty acids of higher molecular weight, preferably those containing 12 to 18 carbon atoms in the acid radical and in particular lauric, myristic, palmitic, stearic, and oleic acids. I have found the so-called metal soaps, such for example as zinc stearate and aluminium stearate, to be particularly eificaceous.

A dyestutf or pigment may also be included with ad- ICE 2 vantage in the composition to indicate clearly the area of metal which has been treated.

' My method is particularly characterised by its ease of application. Having applied the jointing composition to the mating surfaces, there is no need to remove any surplus composition before completing the joint, nor is there any need for any subsequent treatment of the completed joint to ensure a low electrical resistance.

These compositions have the further advantage over previously proposed jointing compositions that they do not require the assembly of the joint to be completed within a comparatively short time after preparation of the contact faces in order to ensure obtaining a joint of high electrical conductivity. In practice it is not always possible'to assemble the joints immediately, and my compositions permit delays of several hours. Thus for example the compositions listed in Table 1 (Lissapol N being the trade name of a commercial wetting agent preparation) ''were applied to the contacting faces in an aluminum bus bar joint. The eifect of this treatment in reducing the contact resistance is shown in the second column of the table, in which the resistance is quoted in arbitrary units, that of a plain bus bar being taken as 1 unit. The third column gives the permissible delay period before the conducti vity becomes adversely atfected.

I have now found that the permissible delay period may be still further increased, particularly when the fatty acid from which the soap employed in the composition is derived is one of the longer chain saturated acids of those hereinbefore quoted, for example stearic or palmitic acid, by the inclusion in the jointing composition of 1 to 6% by weight of a free, liquid fatty acid of higher molecular weight such for example as oleic acid. The preferred proportion is about 2% by weight.

By way of example further jointing compositions are listed in Table 2 (the same arbitrary units being employed as in the examples in Table 1), and the increase in the permissible delay period effected by the presence of the free acid is clearly apparent.

1. Method of forming a mechanical joint between electrical conductors of which at least one is formed from metal or alloy forming a natural oxide skin on exposure to the atmosphere which comprises applying a jointing composition consisting essentially of an aqueous emulsion of an inorganic fluorine-containing compound selected from the group consisting of hydrogen fluoride, bifluorides, boron t'rifluoride, fiuoboric acid and derivatives thereof yielding an acidic reaction in solution in an amount of about 8 percent, a wetting agent selected. from the group consisting of higher acyl derivatives of.

hydroxyand aminov-alkyl sulphonicacids, salts of monosulphuric esters of. higher fatty alcohols, and alkyl derivatives of aromaticrsulphoni'c acids in an amount of about 69 to 71 percent,--a soapfselected from the group consisting of salts of the saturated and unsaturated fatty acids containing from 12 to 18 carbon atoms in the acid radical n an amount f o fire en! a in a t se ec ed from the group consisting of higher acyl derivatives of hydroxyand amino-alkyl sulphonic acids, salts of monosulphuric esters'of higher fatty alcohols, and alkyl derivatives of aromatic sulphonic acids in anamount of about 69 to about 71 percent, a soap selected from the group consisting of salts of saturated and unsaturatedfatty acids containing from 1 2 to 18 carbon atoms in the in an amount of about 20 to 21 percent and 1 percent to 6 percent by weight oleic acid, the pH of the composition. being not greater than 5, to one or both of the mating, surfaces and assembling the conductors in joint relation-1' aqueous emulsion of an inorganic fluorine-containing 2 compound selected from the group consisting of hydrogen fluoride, bifluorides, boron trifiuoride, fluoboric acid and derivatives thereof yielding an acidic reaction in solution acid radical in an amount of about 20 to 21 percent and 1' percent to 6 percent by weight of oleic acid, the pH of the composition being not greater than 5 p I 6. A jointing composition consisting essentially of an 1 aqueous emulsion of fluoboric acid in an amount of about 8 percent, a wetting agent selected from the group consisting of higher acyl derivatives of hydroxyand aminoalkyl sulphonic acids, salts of monosulphuric esters of higher fatty alcohols, and alkyl derivatives of aromatic sulphonic acids in an amount of about 69 to 7 1 percent,

zinc stearate in an amount of about 20 to 21 pereennand 1 percent to 6 percent by weight of oleic acid, the pH'of the composition being not greater than 5.

References Cited in the file of this patent UNITED STATES PATENTS 2,522,937 Forker Sept. 19, 1950 2,553,226 Williams Ma 1s,19 s1,

Miner Ma 2 1 53 

1. METHOD OF FORMING A MECHANICAL JONT BETWEEN ELECTRICAL CONDUCTORS OF WHICH AT LEAST ONE IS FORMED FROM METAL OR ALLOY FORMING A NATURAL OXIDE SKIN ON EXPOSURE TO THE ATMOSPHERE WHICH COMPRISES APPLYING A JOINTING COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS EMULSION OF AN INORGANIC FLUORINE-CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTILNG OF HYDROGEN FLUORIDE, BIFLUORIDES, BORON TRIFLUORIDE, FLUOBORIC ACID AND DERIVATIVES THEREOF YIELDING AN ACIDIC REACTION IN SOLUTION IN AN AMOUNT OF ABOUT 8 PERCENT, A WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF HIGHER ACYL DERIVATIVES OF HYDROXY-AND AMINO-ALKYL SULPHONIC ACIDS, SALTS OF MONOSULPHURIC ESTERS OF HIGHER FATTY ALCOHOLS, AND ALKYL DERIVATIVES OF AROMATIC SULPHONIC ACIDS IN AN AMOUNT OF ABOUT 69 TO 71 PERCENT, A SOAP SELECTED FROM THE GROUP CONSISTING OF SALTS OF THE SATURATED AND UNSATURATED FATTY ACIDS CONTAINING FROM 12 TO 18 CARBON ATOMS IN THE ACID RADICAL IN AN AMOUNT OF ABOUT 20 TO 21 PERCENT AND 1 PERCENT TO 6 PERCENT BY WEIGHT OLEIC ACID, THE PH OF THE COMPOSITION BEING NOT GREATER THAN 5, TO ONE OR BOTH OF THE MATING SURFACES AND ASSEMBLING THE CONDUCTORS IN JOINT RELATIONSHIP SO THAT THE SAID COMPOSITION IS BETWEEN THE SAID SURFACES.
 2. METHOD IN ACCORDANCE WITH CLAIM 1, IN WHICH THE PROPORTION OF OLEIC ACID IS OF THE ORDER OF 2%. 